[
  {"op": "source", "role": "price", "kind": "F64"},
  {"op": "add", "type": "SMA", "name": "fast", "bind": {"length": {"I64": 2}}},
  {"op": "add", "type": "SMA", "name": "slow", "bind": {"length": {"I64": 4}}},
  {"op": "feed", "role": "price", "into": ["fast.series", "slow.series"]},
  {"op": "add", "type": "Sub", "name": "sub"},
  {"op": "connect", "from": "fast.value", "to": "sub.lhs"}
]